Memory devices are widely used in computers and many other electronic items to store information. A memory device usually has numerous memory cells. Some conventional memory devices (e.g., three-dimensional (3D) flash memory devices) have memory cells arranged in tiers, in which the tiers are vertically stacked over a semiconductor substrate. Storage capacity and performance are key features of such memory devices. However, the structures of many conventional memory cells and tiers make improvements associated with device storage capacity and performance difficult. As described in more detail below, the memory devices presented herein include structures that allow them to have improvements over some conventional memory devices.